Rheumatoid arthritis (RA) is one of the most frequent chronic rheumatic diseases affecting large parts of the population. This autoimmune disease causes chronic inflammation of joints, which destroys the joints in the course of time and limits their flexibility.
In general, the treatment of rheumatoid arthritis is staged. First, a patient receives painkillers, which are frequently followed by non-steroid anti-inflammatory drugs (NSAIDs) and disease modifying anti-rheumatic drugs (DMARDs). The last stage of the medical treatment is the use of biological therapies or immune therapies, in order to reduce the ability of the body's immune system to start or maintain unnecessary joint inflammations. As a last measure, operative treatments are performed, resulting in the extreme in artificial joints or operative stiffening of the concerned joints. Especially the immune therapies and operative treatments are very expensive and may cost tens of thousands of dollars per year and patient. Furthermore, drugs used in later stages of treatment can also go along with severe side effects. Since rheumatoid arthritis is a progressive disease, early diagnosis and start of treatment can help postponing adverse effects and high costs of treatment. For deciding on a therapy for a patient, doctors consider a disease activity, e.g. the number and severity of inflamed joints. Thus, a meaningful and intuitive measure of disease activity will help to simplify and accelerate analysis and decision processes for determining an appropriate therapy. Different definitions of disease activity exist for rheumatoid arthritis, most of which are composite indices, such as DAS28, the Health Assessment Questionnaire and others. In the scope of this invention, joint inflammation levels are an important indicator of disease activity.
In rheumatoid arthritis and in many other inflammatory or cancerous diseases, the number and properties of blood vessels in the affected body part are changed, leading to a different perfusion or perfusion dynamics, e.g. in diseased joints. This has been demonstrated, for instance, using time dependent measurements of non-targeted fluorescent dies or other contrast agents. However, in the clinical practice of rheumatologists and other doctors, administration of contrast agents is unfeasible. Moreover, contrast agents are expensive and may be harmful to health or result in immunological reactions.
WO 2010/064202 A2 relates to a device and a method for optical detection of a condition of a joint. An attenuation of light is locally detected for two distinct positions, whereof at least one is the joint to be investigated. Here, the signal resulting from blood can be separated from signals resulting from other sources of light attenuation due to the periodic intensity variations caused by pressure pulses of the patient's blood flow. Since inflamed joints will have a different perfusion and oxygenation compared to healthy joints, the dynamic spectrum behavior will be different.
However, a medical professional has no time for time-consuming analysis of the measured spectra. In particular, although spectra of joints contain information on disease activity, the level of activity is not directly obvious from the measured spectrum. Instead, a medical professional needs an unambiguous and quantitative measure indicating the disease activity as a single value, so that he can make a diagnosis based on the disease activity.